Confirm before inviting unknown users to a DM/room (#33171)

* InviteDialog: factor out startDmOrSendInvites

Factor out the logic of calling `startDm` or `inviteUsers` to a helper
function. We're going to need to call this from a second location soon, so this
is useful groundwork.

* Add `UnknownIdentityUsersWarningDialog`

* Add unit tests

* Update playwright tests

* Convert if/else to switch statement

* Convert helper functions to React components

* Factor out "onRemove" callback

* Add clarifying comment

apps/web/playwright/e2e/crypto/crypto.spec.ts

@@ -27,6 +27,9 @@ const startDMWithBob = async (page: Page, bob: Bot) => {
     await page.getByRole("option", { name: bob.credentials.displayName }).click();
     await expect(page.getByTestId("invite-dialog-input-wrapper").getByText("Bob")).toBeVisible();
     await page.getByRole("button", { name: "Go" }).click();
+
+    await expect(page.getByRole("heading", { name: "Start a chat with this new contact?" })).toBeVisible();
+    await page.getByRole("button", { name: "Continue" }).click();
 };
 
 const testMessages = async (page: Page, bob: Bot, bobRoomId: string) => {